An oleo-pneumatic shock absorbing strut is a known type of shock absorbing strut used in aircraft landing gear. Such a shock absorbing strut typically includes an outer cylinder which defines an inner bore in which a sliding tube is slidably mounted such that the outer cylinder and sliding tube together define a variable sized internal chamber. The chamber contains oil and a gas, such as nitrogen. When the shock absorber is compressed, the chamber volume decreases, compressing the gas and forcing oil through a first damping orifice in order to provide compression damping. The compressed gas serves as a spring, biasing the shock absorber to extend following removal of the compressive force. Recoil damping is provided by the oil passing through a second damping orifice, which can be in the shock absorber annulus.
The oil within an oleo-pneumatic shock absorber is also used for lubrication of the internal sliding surfaces (bearings) between the sliding tube and outer cylinder.
The present inventors have identified that conventional oleo-pneumatic shock absorbing struts can be reduced in weight.